I have a 2008 YZ450F. Bike wasn't running properly after firing it up after sitting for the winter. I did all the minor stuff like checking oils before starting it. Decided to check the valves and the clearance on the intake was out by .10mm on each one. So I took the cams off and metal filings were sitting on top of the shim covers. The head looks destroyed and its scared so bad I cant even remove the shim covers unless I file away some of the overlapping aluminum lol. This is not good.
I am going to have to buy a new head and cams but was wondering if anyone has an idea what caused this so it don't happen again with the new parts. you can see in the pics what happened. Thanks